Cracks in Concrete/Building a Sunroom

My contractor is building a sunroom addition (replacing a kit sunroom that was there when I bought the house). The old concrete patio the previous sunroom was on was not level. Contractor cut out a foot around the 3 edges of the existing pad, dug out trenches, put rebar in, put some rebar in vertically spaced throughout existing pad, built a temp frame around the 3 sides, and poured new concrete, leveling the deck and raising it so that it is nearly at the level of the doorway into the house.

They let it set for 48 hours, then began framing the new sunroom, which is considerably heavier than the old one (was a kit). Now that the roof is on and the windows set in, I just noticed 3 thin cracks running through the concrete (perpendicular to the back wall of my house).

There will be flooring installed over the concrete.

Should I worry about structural issues with those thin cracks?

Size is 12' x 30'. The cracks run down the 12' length. There are no cracks running the opposite direction.

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Anytime you attach a new concrete footing to an old one there is always a chance of cracking. If they did it correctly then it would work in this order.

Drill 8 inch holes in existing footer. Fill cleaned holes wit high strength 2 part epoxy and install rebar. Footer depth should be 12 inches by whatever walls are plus 6". It sounds like he skimmed a thin layer over the old slab which would prob make it below the standard minimum of 3.5 inches. This would easily explain the cracks on top. I dont really see it being a major issue structurally because the outside footer walls are the only ones that matter. Now, if you put something like tile for the sunroom flooring and the concrete continues to settle at an unnatural rate, the tile will crack along with it.

In conclusion, its most likely just the initial settling and i think your in the clear of any further problems.